Introduction to Health Physics: Fourth Edition - Ruang Baca FMIPA UB

INTERNAL RADIATION SAFETY 621
Since the specific activity of the 14 CO is 47.5 × 10 6 Bq (1.28 mCi) per mmol,
the body burden following 2 hours of inhalation is
42 mL
Bq
× 47.5 × 106
22.4 mL/mmol mmol = 8.9 × 107 Bq (2.4 mCi) .
Assuming the blood, and hence the 14 C, to be uniformly distributed throughout
the body of a 70-kg man, the dose rate due to this body burden of 14 Cis
calculated from Eq. (6.47):
˙D =
8.9 × 107 Bq × 1 tps
MeV
× 5 × 10−2
Bq transf × 1.6 × 10−13 J
s
× 3.6 × 103
MeV h
70 kg × 1 J/kg
Gy
= 3.7 × 10 −5 Gy/h (3.7 mrads/h) .
If inhalation had continued until the hemoglobin saturation value were attained,
the body burden would have reached
4.7
3.9 × 8.9 × 107 = 1.1 × 10 8 Bq,
and the dose rate would have proportionately increased to ˙D∞, the maximum
possible value under the conditions of exposure, to 4.5 × 10 −5 Gy/h
(4.5 mrads/h). In this case, the body burden, and hence the dose rate, varied
with time, as shown in Figure 11-8. The instantaneous dose rate during the
period of inhalation (period I in Fig. 11-8) is given by
˙D = ˙D∞
−kt
1 − e i , (11.14)
Figure 11-8. Variation of dose rate with time after start of 14 CO inhalation. Region I under the curve
represents the period of inhalation, and region II represents the period of exhalation. ˙D0 is the dose
rate at the end of the inhalation period, and ˙D∞ is the dose rate due to the saturation amount of
radioactive CO.